Australian salmon

Arripis trutta, known as the Australian salmon in Australia and as kahawai in New Zealand, is a South Pacific marine fish and one of the four extant species within the genus Arripis, native to the cooler waters around the southeastern Australian coasts and the New Zealand coastline. Other common names for this species include Eastern Australian salmon, Eastern Australian mackerel, bay trout, blackback salmon (or just "black back"), buck salmon (or "buck"), cocky salmon, colonial salmon, woolley Judith, newfish and salmon trout.

Although it is referred to as "salmon" in Australian English and its species epithet trutta is Latin for trout, it is not related to true salmons or trouts, which belong to the family Salmonidae of the order Salmoniformes. All Arripis species belong to the family Arripidae of the order Scombriformes.

Habitat

Arripis trutta is a migratory fish that may swim long distances, sometimes thousands of kilometres. The adults congregate and form very large schools off oceanic beaches and exposed coasts coastal areas, and will enter rivers. The juveniles live in smaller schools in more sheltered areas such as bays and estuaries, and these mostly occur in the more southerly areas in which this species occurs. It is carnivorous and feeds mainly on small pelagic fish and crustaceans such as krill. They are highly visual predators, preying on a diverse variety which eat a variety of crustaceans and polychaetes during their juvenile phase, however, adults shift their preferred prey to small schooling baitfish such as pilchards, sprats and anchovies. There is some evidence that the diet of A. trutta has undergone a marked shift since the late 20th century, studies conducted during 1950s and 1960s found that the adults fed largely on krill and squid, which are animals associated with cooler waters. Studies during the early 21st century have shown that the main prey taken is small pelagic baitfish. It is thought that this shift is a result of long-term changes in the East Australian Current which brings warmer waters from the Coral Sea and has extended farther south since the 1990s. It is further thought that this "multi-decadal southward penetration of the EAC" is one of the more obvious indications of global warming and the recorded change in the diet of A trutta forms a biological record of oceanic warming.

Arripis trutta are preyed on by larger marine predators such as seals, dolphins and sharks. The feeding schools push the smaller fish they are preying on towards the surface, making them accessible to seabirds, In this way, this species has an important ecological role in facilitating transfer of energy among the upper levels of the pelagic food chain in inshore ecosystems. An example is the white-fronted tern (Sterna striata) which has the colloquial name "kahawai bird" because often feeds on shoaling fish in association with kahawai, gulls and shearwaters. Fishers hunting for schools of kahawai to troll look out for the flocks of white-fronted terns feeding in association with the predatory fish.

The Australian population of this species spawns in the surf zone between Lakes Entrance in southeastern Victoria and Bermagui in New South Wales South Coast in the late spring and summer. They first spawn when they are around four years old and have attained a length of 39 centimetres (15 in) They can live for up to 26 years.

Distribution

Arripis trutta is found in the southwestern Pacific Ocean mostly around the littoral waters of the Tasman Sea and Bass Strait. In Australia, they are found from Moreton Bay in Queensland to western Victoria and northern Tasmania, with infrequent records at Kangaroo Island in South Australia. They are also found around Lord Howe Island and Norfolk Island in the open waters of the Tasman Sea. In New Zealand, they are distributed around the coasts but are more common north of Kaikōura on the South Island. They are also found around the Chatham Islands and Kermadec Islands east of New Zealand.